High temperature-heat insulator and method for manufacturing three-dimensionally shaped insulator thereof

ABSTRACT

Disclosed is a heat insulator comprising a substrate comprising of a bulk of silica-based inorganic fiber containing a hydroxyl group; a metallic or ceramic infrared mediator held on at least a part of one surface of the substrate; and a silica cured product holding the infrared mediator on/in the substrate. As the infrared mediator, a metal foil or a ceramic particle may be used. This heat insulator exhibits excellent heat insulating performance in a high temperature range of 600° C. or more, and can be molded into a three-dimensional shape which can be directly mounted to a structure.

TECHNICAL FIELD

The present invention relates to an inorganic fibrous heat insulatorexhibiting excellent heat insulating performance at temperatures higherthan 600° C., and a method for manufacturing a three-dimensionallyshaped heat insulator.

BACKGROUND

A device such as a manifold of a motorcycle or automotive, in which acatalyst reaction occurs at a high temperature, is normally covered witha heat insulator for saving thermal energy to secure a reactionefficiency at the high temperature, and for avoiding the affection ofthe high temperature on a device's environment. In recent years, anonwoven fabric or a mat of inorganic fiber such as mineral fiber orglass fiber has been used as a heat insulator due to its lightweight andflexibility. The nonwoven fabric or mat is wrapped around the device forinsulation.

However, wrapping the fiber fabric or mat around the device or acousticabsorber is time consuming and labor extensive. So reducing the time andlabor in the process of covering with an insulator is desired.Additionally, a molded heat insulator having a configuration fitting tothe outer shape of the target device is requested from the operationsite in order to achieve a better fitting to the device and improve heatretaining efficiency. In response to the request, proposed is a methodfor manufacturing an insulator which has a configuration fitting to thetarget device by molding an inorganic fibrous web or a flat substratesuch as fiber mat and blanket into the configuration.

JP4728506B (Patent Document 1) discloses a method for producing a moldedarticle, in which a fibrous web of glass fibers are compressed to adesired shape and kept at a temperature lower than the softening pointby 10-100° C. to melt the contact points between glass fibers, followedby cooling down to solidify the molten contact points of the glassfibers, thereby fixing the shape formed by compression molding.

In this method, glass fibers are fused for molding by heating andpressurizing cotton-or felt-like web of glass fibers.

The glass fiber needs to be melted at least its surface during fusionmolding. According to the method disclosed in the patent document 1, thefusion molding is performed by heating for 10 minutes or more at a hightemperature capable of melting glass fiber, specifically, under thecondition of 780° C. for 30 minutes (first embodiment) or a temperatureof 780 to 810° C. for 15 minutes (second embodiment). However, keepingsuch a high temperature above 700° C. for at least 15 minutes increasesthe cost of the production and hinders the improvement in productivityat a production site. For these reasons, the method may not beacceptable.

Also, as a method for manufacturing a molded heat insulator used in ahigh temperature, U.S. Pat. No. 7,896,943 (Patent Document 2) proposes amethod for producing a conical molded article by placing a binderlessweb of silica-based glass fiber containing Al₂O₃ in a mold, and thenheating at a temperature between 400° F. (204.4° C.) and 1300° F.(704.4° C.) and keeping the temperature for 6 minutes, thereby formingthe web into the conical shape.

Since the silica-based glass fiber containing Al₂O₃ used herein isresistant to a temperature up to 2000° F. (about 1000° C.) and can bemolded without binder, the resultant molded heat insulator can beapplied at high temperatures based on the excellent heat resistance ofthe glass fiber.

On the other hand, selection of an appropriate heating time duration isnecessary according to the heating temperature. Table 1 shows thatmolding under the condition of 1 minute at 1112° F. (600° C.) and 3minutes at 700° F. (371° C.) could not provide a molded article having adesired shape.

Moreover, an inorganic nonwoven fabric or mat made of bulk of mineral-or glass-staple fiber usually contain a shorter fiber than the choppedfiber and/or shot. The shorter fiber is occurred in the production ofthe fabric or mat. The shot is non-fiberized pieces still remained afterthe production of fibers by a blowing method or a spinning method. Suchshorter fibers or shots raise a problem to scatter in the use orapplication of the nonwoven fabric or the mat of inorganic fibers.

In order to solve these problems, it has been proposed to cover thefibrous bulk such as a nonwoven fabric or a mat with metal film.

For example, JP2006-77551A (Patent Document 3) discloses anoncombustible foamed heat insulator in which a foamed substrate isunited with a thin metallic layer at least one surface of the foamedsubstrate through a binder layer. The foamed substrate is formed byentangling a mixture of polyester fiber and a fibrous binder having amelting point lower than the polyester fiber to form into a nonwovenfabric, and then compression-molding the nonwoven fabric into a mat.

This noncombustible foamed heat insulator is not useful for a heatinsulator used at a temperature of 200° C. or higher regardless of itsnoncombustibility based on the cover of aluminum foil because the foamedsubstrate includes polyester fiber.

As a refractory heat insulator applicable to a thermal source having ahigh temperature of 300° C. or higher, for example, JP2017-71084Aproposes a refractory heat-shielding sheet. The heat shielding sheetcomprises of plies as a substrate and a bag made of silica-fiber wovenfabric which packages the plies. The ply comprises a heat-resistantnonwoven fabric of silica-based inorganic fiber containing a hydroxylgroup, and metal layer such as metal foil or metal vapor-deposited film,the metal layer being placed over both sides of the heat-resistantnonwoven fabric. The refractory heat-shielding sheet is durable in useeven at 600° C. thanks to excellent heat resistance of the bag and thenonwoven fabric used as the substrate. Further, since the nonwovenfabric which is a bulk of inorganic fibers is housed in the bag, staplefibers do not scatter.

The laminated state of the plies in which the metal layer disposes onthe nonwoven fabric is secured by housing the plies in the bag.Therefore, if the bag is broken, the laminated state is no longer kept.Furthermore, since the laminated state is not stably fixed, theoperation for housing the plies into a bag and sealing the opening ofthe bag is troublesome. Under the situations, a refractory heatinsulator produceable without a bag is desired for improving theproductivity.

PRIOR ART Patent Document

-   Patent Document 1: JP4728506B-   Patent Document 3: US7896943-   Patent Document 3: JP2006-77551A-   Patent Document 4: JP2017-71084A

SUMMARY OF THE INVENTION Technical Problem to be Solved by the Invention

As described above, the heat insulator made of inorganic fibers can beused at high temperatures and can satisfy the flexibility requirement.However, as for the production of a molded heat insulator of inorganicfibers, a binderless method such as a fusion-molding method utilizingfusion of glass fibers is time consuming and is unsatisfactory in termsof productivity.

According to the method of heat setting with use of a special glassfiber as proposed in the patent document 2, time duration for heatsetting can be shortened without impairing the heat resistance at hightemperatures inherent in glass fiber, but reducing the time duration to5 minutes or less has not been achieved yet. The reduction of the timeduration to below 5 minutes is required from the production site forproductivity.

A nonwoven fabric or a mat formed by entangling fibers has a largeporosity and large pores. Thus the nonwoven fabric or a mat requires alarge amount of energy for keeping high temperatures because of theleakage of radiant thermal energy through the pores.

Under these situations, the present invention has been achieved. Thepurpose of the invention is to provide an inorganic fiber heat insulatorhaving excellent heat resistance usable at a temperature above 600° C.,and capable of directly forming into a three-dimensional shape fittingto a device used for high temperatures. Also, the present invention isto provide a method of imparting a three-dimensional shape within 5minutes so as to satisfy a requirement of productivity.

Means for Solving the Problem

The heat insulator for high temperature of the invention comprises asubstrate comprising of a bulk of silica-based inorganic fibercontaining a hydroxyl group; a metallic or ceramic infrared mediatorheld on at least a part of one surface of the substrate; and a silicacured product holding the infrared mediator on/in the substrate.

The infrared mediator is a metal foil having a thermal emissivity of 0.3or less or a ceramic particle having a thermal emissivity of 0.6 to 0.9.

Therefore, according to one aspect of the invention, embodiments of thehigh-temperature-heat insulator of the invention includes

-   (I) metal foil-adhering type heat insulator wherein the infrared    mediator is a metal foil having a thermal emissivity of 0.3 or less,    and the silica cured product is a solidified material containing a    layered silicate and silica powder;-   (II) particle dispersion type heat insulator wherein the infrared    mediator is a ceramic particle having a thermal emissivity of 0.6 to    0.9, and the silica cured product is an inorganic polymer containing    siloxane bond; and-   (III) a combination type heat insulating material having both    embodiments (I) and (II).

In the embodiment (I), the metal foil is preferably adhered to thesurface on the opposite side to a thermal source to be insulated. In theembodiment (II), the ceramic particles are preferably held on/in thesurface which faces a thermal source to be insulated.

According to the invention, the method for manufacturing a hightemperature-heat insulator having a three-dimensional shape from a flatsubstrate of a silica-based inorganic fiber containing a hydroxyl group,comprising steps of A) providing the flat substrate with an infraredmediator by the step a-1) and/or a-2): and

a-1) coating, applying, spraying or impregnating a colloidal solution inwhich amorphous silica particles and particulate infrared mediator aredispersed in an aqueous medium,

a-2) coating, applying, spraying or impregnating a suspension or pasteeach containing a film-forming component and silica powder, on onesurface of the flat substrate, and thereafter attaching a film-likeinfrared mediator to the surface; B) heating and compressing the flatsubstrate to form into a three-dimensional shape.

Effect of the Invention

According to the heat insulator of the invention, the infrared mediatoris held on a surface or surface layer of the fibrous substrate ofsilica-based inorganic fibers. Therefore, the infrared mediator mayreflect or absorb infrared rays contributing to high temperature and maysuppress the leakage of infrared rays to its surroundings. In additionto the effect of the suppression of the leakage by the infraredmediator, pores between fibers in the substrate may provide a heatinsulating effect. Therefore, an excellent heat insulating effect can beobtained. Moreover, the silica cured product for holding the infraredmediator may support to sustain the imparted shape. Furthermore, in thecase that the metal foil used as the infrared mediator is disposed tothe external side of the heat insulator, the metal foil may suppressscattering of the short fiber and/or shot from the substrate, and mayalso suppress the intrusion of foreign matters such as dust and sandfrom its surroundings, as well as may avoid the foreign matter fromattaching to the substrate.

According to the method of manufacturing the high temperature-heatinsulator of the invention, not only the infrared mediator can be heldin the substrate, but also a desired shape can be imparted to the heatinsulator. Therefore, the method can provide a heat insulator having adesired three-dimensional shape with excellent productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for showing processes of manufacturing a particledispersion type three-dimensionally shaped heat insulator.

FIG. 2 is a schematic diagram of a metal foil-adhering type heatinsulator.

FIG. 3 is a diagram for showing processes of manufacturing metalfoil-adhering type three-dimensionally shaped heat insulator.

FIG. 4 is a schematic diagram for showing the method of evaluating heatinsulating performance executed in Example.

FIG. 5 is a schematic diagram for showing a method of evaluating shaperetention property executed in Example.

FIG. 6 is a microscope photograph of the particle dispersion type heatinsulator.

FIG. 7 is a microscope photograph of a substrate alone.

FIG. 8 is a schematic diagram for showing the configuration of the metalfoil-adhering type heat insulator prepared in Example.

FIG. 9 is a photograph of the metal foil-adhering type heat insulatorprepared in Example.

EMBODIMENT FOR CARRYING OUT THE INVENTION

The high temperature-heat insulator of the invention comprises asubstrate comprising of a bulk of silica-based inorganic fiberscontaining a hydroxyl group; a metallic or ceramic infrared mediatorheld on at least a part of one surface of the substrate; and a silicacured product holding the infrared mediator in/on the substrate.

Each component will be described below.

[Substrate]

The substrate used in the invention is a bulk of silica-based inorganicfiber containing a hydroxyl group. The bulk is normally in a form ofnonwoven fabric, mat, felt, or the like, in which filaments or staplesof a silica-based inorganic fiber containing a hydroxyl group areentangled. Among these, a needle-punched mat is preferable. Theneedle-punched mat is formed by needle punching a flat web to entanglethe fibers and stabilize the web with a certain thickness.

Not only one kind of the silica-based inorganic fiber, but also acombination of two or more of them may be used for the substrate.

A preferable silica-based inorganic fiber containing a hydroxyl groupfor the substrate is silica fiber containing 0.1-20% of Al₂O₃ and80-99.9% of SiO₂. The silica-based inorganic fiber is appropriate due toexcellent compatibility to water glass (sodium silicate solution) andsilica particles, which are primary components of binder. Thesilica-based inorganic fiber is also compatible to silicate as afilm-forming component.

The silica-based inorganic fiber containing a hydroxyl group is aheat-moldable glass fiber containing 81 wt % or more of SiO₂, andcontaining Si(OH) in a part of SiO-based network. The hydroxyl groupseems to be remained in the production of filament or staple fiber froma starting glass material by proton exchange of a metal or metal oxideion (e.g. Al³⁺, TiO²⁺, T⁴⁺, ZrO²⁺ or Zr⁴⁺) contained in the startingglass material. The hydroxyl groups contained in the silica-basedinorganic fiber form a new siloxane bond (Si—O—Si bond), and releaseH₂O, through a condensation reaction at about 600-800° C., as indicatedby the formula (1) below.

[Formula 1]

Si(OSi)₃OH+HO—Si→Si(OSi)₄+H₂O   (1)

A typical silica-based inorganic fiber containing hydroxyl group has acomposition represented byAlO_(1.5).18[(SiO₂)_(0.6)(SiO_(1.5)OH)_(0.4)]. A commercially availablefibers may be used. For example, BELCOTEX® from BELCHEM GmbH may beused.

The BELCOTEX® fiber is typically made from silicic acid-modified withalumina. A standard type of staple fiber preyarn has an average finenessof about 550 tex. The BELCOTEX® fiber is amorphous and generallycontains about 94.5 wt % of silica, about 4.5 wt % of alumina, less than0.5 wt % of an oxide, and less than 0.5 wt % of other components. Thefiber has an average diameter of about 9 μm with little variation, amelting point of 1500 to 1550° C., and heat resistance up to 1100° C.

Silica-based inorganic fibers containing hydroxyl groups other thanBELCOTEX® may be used by an appropriate selection according to thepurpose of its use and application.

The diameter of the silica-based inorganic fiber is from 6 to 13 μm,preferably from 7 to 10 μm. The length of the inorganic fiber depends onthe form (felt, nonwoven fabric, blanket, sheet, etc.) of the substrate.The staple fiber having a length of commonly from 1 to 50 mm, preferablyfrom 3 to 30 mm or the filament having a length of commonly from 30 to200 mm, preferably from 50 to 150 mm, may be used.

When a needle-punched mat is used for the substrate, a preferable fiberlength is from 30 to 130 mm, more preferably 45 to 100 mm from theviewpoint of mat formability by needle-punching.

The fiber sheet or flat web for a substrate has a thickness of about 3to 25 mm, preferably 3 to 12 mm, and more preferably 4 to 10 mm. In thecase of producing by compression molding, the use of an unduly thinsheet or web may provide an insulator having an insufficient thicknessso that the resulting insulator may not achieve a desired heatinsulating performance and/or sufficient strength. On the contrary, theuse of an unduly thick sheet or web tends to be difficult in forminginto a desired shape and the resulting insulator tends to be poor inshape retention.

The density of the substrate is preferably from 80 kg/m³ to 180 kg/m³,and more preferably 90 kg/m³ to 160 kg/m³. If the density is too high,compression molding becomes difficult. On the other hand, if the densityis too low, shape retention of the molded insulator is lowered, and thestrength of the resulting insulator is insufficient. The heat insulatingperformance also tends to be lowered.

[Infrared Mediator]

The infrared mediator contributes to a heat insulating performance byabsorbing or reflecting infrared rays, primarily near-infrared rays(wave length: about 1 μm to about 4 μm). The infrared rays are relevantto thermal energy at high temperatures.

The heat transfer is classified into three types: convection,conduction, and radiation. Among them, the ratio of heat transfer byradiation is relatively high at a temperature above 500° C. Therefore,the heat insulator to be used at high temperatures of 500° C. or more,preferably 600° C. or more, and more preferably 800° C. or more, iseffective to suppress the leakage of the thermal energy near the thermalsource to its surroundings. The infrared mediator used in the inventionmay prevent leakage of infrared rays emitted from the thermal source byreflecting them. Alternatively, the infrared mediator may absorb thethermal energy of the thermal source and radiate it in the vicinity ofthe thermal source, thereby suppressing the energy consumption of thethermal source.

According to an exemplary embodiment of the invention, the infraredmediator may be (1) a metal foil having a thermal emissivity (ε) of 0.3or less used as a reflection type infrared mediator, or (2) a ceramicparticle having a thermal emissivity of 0.6 to 0.9 used as an absorptiontype infrared mediator. These will be described in detail below.

(1) Reflection Type Infrared Mediator

As a reflection type infrared mediator, a metal foil having a thermalemissivity of 0.3 or less, preferably 0.2 or less, and more preferably0.1 or less may be used. A metal having metallic luster may normallymeet a thermal emissivity of 0.3 or less.

Metal foil covering one surface of the heat insulator can reflectinfrared rays emitted from the thermal source and suppress leakage ofinfrared rays to its surroundings. In the case of a metalvapor-deposited film, a pinhole may be formed in the deposition layer ofthe metal depending on the thickness of the deposition layer.Alternatively, a metal layer formed by vapor deposition is readily togenerate a pinhole when a three-dimensional shape is formed. The pinholecauses the leakage of infrared rays. On the other hand, metal foil isfree from a pinhole before it is torn. Therefore, the metal foil canexhibit excellent reflection effect of the thermal energy from thethermal source.

When a heat insulator has a metal layer held on the thermal source side,a metal having a melting point equal to or higher than the thermalsource temperature, preferably a metal having heat resistance as high asthat of the substrate, may be used for the metal layer. Specifically, amelting point of the metal is 800° C. or higher, preferably 1000° C. orhigher, more preferably 1200° C. or more, and still more preferably1500° C. or higher. On the other hand, when a heat insulator has a metallayer held on the external side which is the opposite side to thethermal source, a metal having heat resistance lower than a metal foilheld on the thermal source side may be applicable. Because the ambienttemperature is lower than the thermal source temperature due to the heatinsulating effect of the substrate. Therefore, a metal having a meltingpoint of 400° C. or higher as well as 600° C. or higher may be useddepending on the thermal source temperature and the kind of thesubstrate (particularly its thickness).

Examples of the metal foil to be used include aluminum foil, silverpaper, titanium foil, stainless foil, nickel foil, copper foil, phosphorbronze foil, brass foil, nickel silver, permalloy foil, inconel foil,nichrome foil, molybdenum foil, zirconium foil, tantalum foil, tin foil,zinc foil, indium foil, niobium foil, lead foil, and plated iron foil.

The metal foil to be used may be appropriately selected according tocharacteristics such as melting point, ductility, and thickness, and thetype of heat insulator in which the metal foil is used. In the case ofthree-dimensionally shaping, the metal foil to be used is appropriatelyselected taking into consideration the final shape, in particular, thesize of R portion of the shaped insulator.

As the metal foil, aluminum foil, gold paper, copper foil, stainlesssteel foil, molybdenum foil, and inconel foil are preferably usedbecause of their thermal emissivity of 0.3 or less and excellentductility. Also, from the viewpoint of low thermal emissivity, apreferable metal foil is a specular glossy metal foil whose surface isnot oxidized and is not subjected to matte processing.

The thickness of the metal foil is 5-150 μm, preferably 10-100 μm, andmore preferably 20-50 μm. A metal foil as thin as 5 μm or less is poorin handling property and would be readily broken. On the other hand, athick metal foil with a thickness above 150 μm is poor in ductility aswell as in three-dimensional moldability.

(2) Absorption Type Infrared Mediator

As the absorption type infrared mediator, a ceramic particle having athermal emissivity of 0.6 to 0.9, preferably 0.65 to 0.85, may be used.

A ceramic particle having an average particle size of 0.5 to 4 μm,preferably 1 to 3 μm, and more preferably 1 to 2.5 μm may be used. Theaverage particle size is measured by the light scattering method.Preferably, the ceramic particles may have a cumulative 90% diameter(D₉₀) of 10 μm or less, preferably 8 μm or less, and more preferably 7μm or less in particle size distribution. The ceramic particles fallingin the size range can absorb infrared rays, especially near-infraredrays, and radiate it. Therefore, the consumption of thermal energy fromthe thermal source can be suppressed if the absorption type infraredmediator is contained in the heat insulator and is held at a closerportion to the thermal source.

Since a ceramic particle is placed near the thermal source for utilizingas an infrared mediator, it is preferable to select a ceramic particlewhich is hardly oxidized and molten even after long-term exposure tohigh temperatures. The ceramic particle should have a melting point of1500° C. or higher, and includes carbides, nitrides, and borides. Carbongraphite has such a high melting point and high thermal emissivity,however, the carbon graphite particle may not be used as an infraredmediator. This is because the carbon graphite particle usually hasemissivity (ε) higher than 0.95, and could not almost reflect infraredrays, which might overheat a limited portion around the carbon graphiteparticle. Moreover, carbon graphite has an extremely high thermalconductivity comparing to silica-based fibers and ceramic particles.Once the carbon graphite reaches a high temperature, heat transfer dueto heat conduction through carbon graphite becomes large. On the otherhand, a ceramic particle held in the silica cured product is capable ofmoderately reflecting infrared rays due to a refractive index differencebetween the ceramic particle and the silica cured product. Additionally,since the ceramic particle has a smaller thermal conductivity than thatof metal or carbon graphite, the ceramic particle is likely to provideheat insulating effect due to its absorption or radiation of infraredrays. However, if the ceramic particle has an unduly large size, theceramic particle itself may act as a heat emittance. For these reasons,the ceramic particle is preferable to have a size sufficient enoughabsorbing near-infrared rays.

Examples of ceramics used as an absorption type infrared mediatorinclude carbides such as WC, TiC, SiC, and ZrC; nitrides such as TiN,ZrN, and TaN; borides such as CrB, VB₂, W₂B₅, WB, TaB, and MoB; andsilicide such as TiSi, ZrSi, and WSi. In general, a melting point ofthese ceramic particles is 1500° C. or more, and the melting point ofcarbide, nitride, and boride particles is 2000° C. or more. Theseceramic particles allow to use the heat insulator at high temperaturesbased on the heat resistance of the substrate. Among these, siliconcarbide, silicon nitride, and silicon boride are preferable from theviewpoint of affinity to the silica cured product, and SiC is morepreferable.

Such ceramic particles are held in the surface part of the substratethrough the dispersion in the silica cured product or by attaching tothe surface of silica-based inorganic fiber in the substrate, or beingtrapped in the space between the silica-based inorganic fibers of thesubstrate.

In order to stably fix and hold the ceramic particles in a surface partof the substrate with the silica cured product, the content of theceramic particle as the infrared mediator is preferably from 1 to 20% byweight, more preferably 2 to 15% by weight, and even more preferably 3to 10% by weight, based on the weight of the silica cured productcorresponding to the solid content of colloidal silica. When thequantity of the ceramic particle is too small, the infrared absorptioneffect is not satisfactory. When the quantity of the ceramic particle istoo large, the particles tends to form a flocculate, which may affectinsulation due to the thermal conduction of the ceramics itself, as aresult, the infrared absorption effect is lowered.

[Silica Cured Product]

A silica cured product which makes a role of fixing and holding aninfrared mediator is an inorganic polymer containing SiO₂ or Si—O—Sibond (siloxane bond). According to an exemplary embodiment of theinvention, the silica cured product may be a dry solidified product offilm-formable fluid containing silica powder or a dry solidified productof a silica colloid solution such as colloidal silica.

Such a silica cured product has heat resistance almost similar to thatof the silica-based inorganic fiber, and can stably hold the infraredmediator at high temperatures.

(1) Dry Solidified Product of Film-Formable Fluid Containing SilicaPowder (Film-Forming Silica-Based Binder)

When a film-like infrared mediator such as metal foil is adopted, thesilica cured product needs to act as a binder between the metal foil andthe substrate. The film-formable fluid containing silica powder for asilica-based binder is a viscous liquid (suspension) or paste containinga film-forming component in a silica powder-dispersing fluid, or amixture of water glass and this.

(1-1) Silica Powder-Dispersing Fluid

Examples of the silica powder include a pulverized product ofcrystalline silica (e.g. quartz powder, silica sand, silica stone,moringite, cristobalite), and amorphous silica (e.g. colloidal silica,precipitated silica, dry silica, fumed silica). A hydrous amorphoussilica such as opal may also be used.

The silica may be synthetic silica or a mineral-containing silica.

Examples of dispersion medium of the fluid include water, water glass,organic solvents (e.g. lower alcohols such as isopropanol; esters suchas ethyl acetate; ethers such as ethylene glycol monopropylether andpropylene glycol monomethyl ether; ketones such as methyl ethyl ketoneand methyl isobutyl ketone; cycloalkanes such as cyclohexanone; aromaticcompounds such as toluene); and mixtures of water and a lower alcohol(e.g. methanol, ethanol, propanol, isopropanol); and a combination ofthem.

The water glass is a condensed aqueous solution having a high content ofsodium silicate, and has a puddle-like viscosity. Although the waterglass may be film-formable, the water glass may not be chosen for use ata temperature higher than 700° C. due to its relatively low meltingpoint and softening point. Therefore, in the case of the metalfoil-adhering type heat insulator used at a temperature above 700° C., apreferable heat insulator adopts a silica-based binder using a mixtureof water and a lower alcohol as a dispersion medium.

In addition to the silica powder, the dispersion medium may contain aceramic powder such as alumina powder within 30% or less, preferably 20%or less, more preferably 10% or less, and more preferably 5% or less ofthe solid content in the fluid. These content ranges do not affect theadhesiveness.

The solid content or the solid amount contained in the fluid isappropriately selected depending on either paste or suspension. Inparticular, when the binder is applied to a substrate by coating,applying, spraying or the like, the viscosity of the binder isappropriately adjusted for applying operation.

As the dispersion medium containing silica powder, a commerciallyavailable product as a heat-resistant inorganic adhesive may be used.Examples of the commercially available products include BETACK series(BETACK#160 CC, BETACK #900B, BETACK #900C, BETACK #1200, BETACK #1550B,BETACK #970, BETACK #1600S, BETACK #1800 LB, BETACK #003, BETACK #870,and BETACK #873) from Sakai Chemical Industry Co. Ltd., and so on.

(1-2) Film-Forming Component

A layered silicate is used as a film-forming component for imparting afilm-forming property to the silica powder-dispersing fluid as describedabove. The silica powder-dispersing fluid, particularly a suspension orpaste in which water is used as a dispersion medium, is dried andsolidified to turn into silica powder flocculate. The silica powderflocculate is likely to collapse and fall off from the silica curedproduct upon impact, bending, abrasion, and the like. When water glassis used as a dispersion medium, the resulting glass is softened at ahigh temperature, and the force holding the silica powder may belowered. On the other hand, the layered silicate can make a role of afilm forming component which is capable of preventing the silica powderfrom falling off and scattering.

The layered silicate is also referred to as a phyllosilicate, in which atetrahedron of SiO2 is connected to each other to form a planar layeredstructure by sharing three oxygen atoms at the corners of thetetrahedron.

The metal constituting the silicate salt includes aluminum, potassium,sodium, calcium, and magnesium.

As the layered silicate, a sodium silicate represented by xNa₂.ySiO₂(y/x=from 2 to 3) is preferable. Minerals such as smectites (e.g.saponite, hectorite, stevensite, and montmorillonite), permeances, orthe like may be used, and smectites are preferably used.

A material containing a layered silicate may be used as a film-formingcomponent. As the layered silicate, not only a synthesized layeredsilicate but also a mineral such as a smectite or a permeance, orbentonite primarily containing the mineral may be used.

Alternatively, a natural bentonite as well as a purified bentonitehaving an increased content of montmorillonite as a main component byremoving impurities from the natural bentonite may be used. Further, asynthetic bentonite which contains sodium bentonite converted fromcalcium bentonite by ion exchange may be used. Bentonite is a genericterm of clay containing montmorillonite as a main component.

Such a layered silicate is swollen by water absorption when dispersed inwater. Further, the cation contained between layers of the layeredsilicate is hydrated with water molecule, thereby the layered silicateto divide into individual layers. A hydrated layer is formed on thesurface of the resulting single layer to become viscous. As a result, athickening effect is appeared. Further, the layered silicate is presentin a state of aqueous dispersion (suspension), which acts likethixotropic fluid, thus, the viscosity of the suspension is high in thelow shear region while the viscosity of the suspension is lowered in thehigh shear region.

The content of the film-forming component in the silica cured product ispreferably 0.1-5% by weight, preferably 0.5-4% by weight, and morepreferably 1-3% by weight.

The amount of the above range is sufficient for the film-formingcomponent to make its role. Unduly high content causes the viscosity ofthe suspension extremely high, which limits to a coating method or thelike for applying the dispersion to the substrate. So the workabilitytends to be deteriorated.

The film-forming silica-based binder having the above-describedcomposition is a viscous and thixotropic fluid (suspension, viscousliquid, or paste). When the binder is solidified, the layered silicateis solidified with a stable card structure. When the silica powderdispersion as a main component of the silica-based binder is dried andsolidified, the layered silicate is filled between the aggregates ofsilica particles. It is considered that the silica particles are stablyheld in the solidified layers, to prevent the silica particles fromscattering.

Thus film-forming silica-based binder is dried and solidified to turninto a silica cured product in which the silica powder disperses in afilm-forming component as a matrix. The silica powder dispersed in thefilm-forming component can act for a binder through which the metal foilis bonded to the silica-based inorganic fiber. When water glass iscontained, the metal foil can be bonded to the silica-based inorganicfiber of the substrate in the process of vitrification (solidification).

(2) Colloidal Solution (Colloidal Silica) in which Particles ofAnhydrous Silicic Acid are Dispersed

Colloidal silica is a colloidal solution in which aggregate of silicondioxide (SiO₂) containing an OH group formed by hydration on its surfaceis dispersed in an aqueous dispersion medium in a form of colloidalparticle.

Water and/or an organic solvent are used as the dispersion medium.Example of the organic solvent include lower alcohols such asisopropanol; esters such as ethyl acetate; ethers such as ethyleneglycol monopropylether and propylene glycol monomethyl ether; ketonessuch as methyl ethyl ketone and methyl isobutyl ketone; cycloalkanessuch as cyclohexanone; aromatic compounds such as toluene. A mixture ofwater and a lower alcohol (e.g. methanol, ethanol, propanol,isopropanol) may be used. Among them, an aqueous dispersion medium suchas water, or a mixture of water and a lower alcohol are preferably usedfrom the viewpoint of working environment.

The colloidal particles are stably dispersed in aqueous dispersionmedium because SiOH groups and OH-ions present on the surface of theamorphous silicon dioxide particles can be stabilized due to coexistenceof alkali ions such as Na ion.

In such a colloidal particle as a dispersoid, a siloxane bond is newlyformed from the SiOH groups, when the dispersion medium is evaporated byheating. And then the colloidal particles are integrated or fused on thesurface of the colloidal particles, thereby acting as a binder betweensilica-based inorganic fibers in the substrate.

The content of silicon dioxide in the colloidal solution, or solidcontent of the colloidal solution, is from about 5 to 60% by weight,preferably 5 to 50% by weight, and more preferably 10 to 40% by weight.In the case of spray method, a colloidal solution having a viscosity of300 mPa·s or less is preferred from the viewpoint of working efficiency.

The lower the content of silicon dioxide (solid content), the moreincreased amount of coating for assuring the necessary amount of silicondioxide for keeping the shape of the molded body. A larger amount ofcoating requires a larger energy for evaporation of water contained inthe dispersion medium when heat molding. Also, a longer period forheating is disadvantageous in productivity improvement. On the otherhand, an insufficient amount of coating may result in a molded bodyhaving unsatisfactory strength.

If the content of silicon dioxide (solid content) is too high, thesilicon dioxide powder remaining on the surface of the molded body tendsto increase. The remained silicon dioxide powder becomes dust and lowershandling property. In addition, stability of colloidal particles as adispersoid is lowered to be gelled easily in a state of suspension ordispersion before molding. For these reasons, the colloidal solutionhaving too high content of silicon dioxide is used by coating orapplying method instead of spraying, although they are poor inapplication workability. Moreover, the colloidal solution having undulyhigh solid content tends to be hard for silicon dioxide to intrude intothe substrate and exhibit excellent binder function for keeping animparted shape.

The size (average particle diameter) of the colloidal particles is notparticularly limited, but is normally from 1 to 200 nm, preferably 2 to100 nm, more preferably 3 to 50 nm, still more preferably 4 to 25 nm,and particularly preferably 4 to 18 nm. The increase of the particlesize decreases the number of particles when the content is the same,therefore the strength of the resulting molded insulator tends to belowered. Further, shape retention property of the molded insulator tendsto be deteriorated.

The average particle size as used herein is an average of primarycolloidal particle, and can be obtained in terms of sphere equivalentdiameter by dynamic light scattering method, shearing method, BETmethod, laser diffraction scattering method, or the like. The measuringmethod may be appropriately selected depending on the size of thecolloidal silica. For example, particles of several tens nm or less arepreferably used by a BET method or a laser diffraction scatteringmethod. The particle size measurement by the dynamic light scatteringmethod may be performed using a commercially available particle sizedistribution measuring apparatus. The shearing method is disclosed inAnalytical Chemistry, vol. 28, pp1981-1983 (1956), and is common in ananalysis technique applied to the measurement of the average particlesize of colloidal silica.

The colloidal particles may exist in a form of individually dispersedspherical particle or in a form of chain-like or beads-like aggregatewhich is formed by association of particles.

The chain- or beads-like aggregate may be a secondary particle extendingin one direction like chain, or may form an extended secondary particleby bonding through condensation between their silanol groups. Theextension form may be linear, branched, or partial mesh.

Such chain-like, thread-like, or beads-like aggregate has an averagediameter (secondary particle diameter) falling in the above-mentionedrange of the particle average diameter when the aggregate is assumed asa sphere. Such a secondary particle size can be measured by a dynamiclight scattering method. The average particle diameter of the colloidalprimary particles (spherical particles) constituting the secondaryparticle is preferably from 4 to 18 nm.

The aggregate or associated particles as the colloidal particle islikely to provide a rigid film, which is advantageous in retention ofthe three-dimensional shape imparted by molding. On the other hand, inthe case where the average particle diameter is increased or achain-like or beads-like aggregate is formed, a larger particle or thechain- or beads-like aggregate does not tend to intrude into thesubstrate and remains on the surface layer of it. This means that therate of the particles or aggregates remaining on the surface of themolded insulator tends to increase. They turn into powder by heatsetting and cause a problem associated with dust. From the viewpoint ofhandling ability, a preferable colloidal solution is a solution in whicha sphere particle having a smaller particle size is dispersedindividually as a dispersoid.

An unduly large colloidal particle as the dispersoid is difficult toimpregnate into the flat substrate of the inorganic fibers, which maylower the function of the binder for shape retention. From thisviewpoint, a preferable average particle diameter (primary particlediameter) of the colloidal silica is relatively small.

The stability of the colloidal particles is generally susceptible to pHof the colloidal solution. For preventing gelation, the colloidalsolution is preferable to be stabilized with an alkali, specifically, Naion. The liquid property (pH) of the silica colloid solution is relatedto the stabilization of the colloidal particles. When stabilized with Naions, the dispersion is normally alkaline having pH of 8 to 11. Also,the neutral or acidic dispersion having pH of 4 to 7, which may beattained by reducing the quantity of strong alkali ions for stabilizingthe colloidal particles, may be employed.

The specific gravity at 20° C. of the colloidal solution is usuallydependent on the silica content. When the silica content is adjusted tothe above-mentioned range, the specific gravity falls in the range of1.10 to 1.40, and preferably about 1.12 to 1.25.

Further, a preferable viscosity at 25° C. is 300 mPa·s or less, morepreferable viscosity is 100 mPa·s or less.

In general, a colloidal solution having a higher viscosity is likely tobe gelled, and is difficult to apply to the substrate by a spray methodas described later. A preferable viscosity is 80 mPa·s or less, further60 mPa·s or less from the viewpoint of workability and productivity.

The colloidal silica or a colloidal solution of silicon dioxide used inthe invention may contain a slight amount (about 500 to about 300 ppm)of a divalent metal such as calcium, magnesium, Sr, Ba, Zn, Pb, Cu, Fe,Ni, Co, Mn, and/or a trtivalent metal such as Al, Fe, Cr, Ti, and Y in asilica sol derived from the material used in the production of thecolloidal silica.

[Embodiment of High Temperature-Heat Insulator]

According to the invention, the high temperature-heat insulatorcomprising a substrate, an infrared mediator and a silica cured productinclude the embodiments below:

-   (I) a metal foil-adhering type heat insulator which adopts a    reflection type infrared mediator such as metal foil;-   (II) a particle dispersion type heat insulator which adopts an    absorption type infrared mediator such as ceramic particle; and-   (III) a combination type heat insulator which adopts both of a    reflecting type infrared mediator and an absorption type infrared    mediator.-   These heat insulators and a method for manufacturing a respective    three-dimensionally shaped article will be described below.

<Particle Dispersion Type Heat Insulator and Method for Manufacturing aThree-Dimensionally Shaped Article>

In the particle dispersion type heat insulator, a silica cured productis present in a state of adhesion to the surface of the fiberconstituting the substrate, or being embedded in a space between thefibers, or crosslinking between the fibers in the substrates. Thereby,the ceramic particles may be held in a space between fibers or in thesilica cured product.

The molded insulator having a three-dimensional shape can be produced bythe following manufacturing method.

The method for manufacturing a particle dispersion type heat insulatorhaving a three-dimensional shape comprises a step of coating, applying,spraying or impregnating a silica colloid solution containing anabsorption type infrared mediator (ceramic powder) on one surface of aflat substrate of silica-based inorganic fibers; and a step of heatingand compressing the flat substrate to form a surface into a recessedpart of the three-dimensionally shaped insulator.

Each step will be described below with reference to FIG. 1

(1) Application Step of Silica Colloid Solution Containing CeramicParticles

The application step is carried out by coating, applying, spraying orimpregnating a silica colloid solution containing ceramic powder as aparticulate infrared mediator on one surface of a flat substrate 1 whichis fibrous board of silica-based fibers. The selection from coating,applying, spraying or impregnating is done according to the viscosityand the solid content of the silica colloid solution.

The application may be carried out by brushing; a roll coater methodusing doctor blade, gravure coater, or the like; screen printing using asqueegee; spray coating using an air spray gun, airless hand spray,pressure-feed type automatic air spray or the like; and contact methodsoaking the one surface in the silica colloid solution.

Of these, the spray coating is preferred in workability andproductivity. For example, FIG. 1(a) shows a method of spraying thecolloid solution 2 from the upper side of a flat substrate 1 comprisingof bulk of silica-based inorganic fibers 1 a. FIG. 1(b) shows a state inwhich the silica colloid solution containing the particulate infraredmediator 2 a is coated on one surface of the flat substrate 1.

The amount of the silica colloid solution to be coated is appropriatelydetermined according to the solid content of the solution. Accordingly,the amount of coating is from 100 to 600 g/m², preferably from 100 to400 g/m², more preferably from 100 to 300 g/m² in terms of solid contentper coated area of the substrate.

If the amount (solid content) is too large, the silica colloid particlesor the ceramic particles are hardly impregnated into the moldedinsulator, so that a silica layer is likely to be formed on one surface(coated surface) of the molded insulator. Thus resulting rigid silicalayer is poor in flexibility and cushioning property compared to thesubstrate of inorganic fibers, as a result, mounting workability of theobtained heat insulator is lowered. Moreover, the ceramic particles asthe infrared mediator cannot be stably held. Even when relatively smallcolloidal silica particle which is apt to intrude into the fibrous boardis used, an unduly large amount of coating increases the quantity ofsilica powder remained on the surface of the substrate in the moldedinsulator. As a result, handling property and workability is lowered dueto powdery dust.

The silica colloid solution having unduly low concentration (solidcontent) increases its amount of coating for assuring a desired solidamount. The increase in the amount prolongs time period for drying aswell as heating for curing, which results in lowering the productivity.Reducing the amount of coating for productivity reduces the amount ofsilica served as a binder. Therefore, the retention of the impartedthree-dimensional shape would be difficult.

(2) Heating and Compressing Step

A step of heating and compressing a colloidal silica-coated substrate istypically carried out by setting the substrate in a mold heated to acertain temperature. The substrate is preferably set in a state wherethe silica colloid solution-coated surface is positioned at a concaveside of the resulting three-dimensional shape.

For example, when a pair of molds, i.e. male mold 5 and female mold 6are used as shown in FIG. 1(b), a convex of the male mold 5 and thecolloidal silica 2 a coated surface are set to become face-to-face. Thesubstrate is pressed against the female mold 6 with heating through themale mold 5, a resulting insulator 7 has a configuration fitting to theconcave of the female mold 6 (FIG. 1(c)).

The pressure force in the compressing step is a pressure to reduce thethickness of the substrate by below 50%, preferably the range of 5 to45%, and more preferably the range of 10 to 40%. The reduction ratecorresponds to a ratio of the thickness reduction (T₁-T₂) to theoriginal thickness of the substrate (T₁) which is 100% (see FIG. 1(a)),wherein T₂ represents the thickness after compression (see FIG. 1(c)).

The larger reduction in thickness means a larger compression rate of thesubstrate in the compressing step. If the compression ratio is toolarge, the inorganic fiber constituting the substrate is apt to recoverthe original thickness due to its resilience, and the imparted shape maynot be retained. Additionally, a thicker insulator is superior in heatinsulating performance. On the other hand, when the thickness reductionrate is too low or the compression rate is too small, the ratio ofimmobilized fibers is lowered because the silica colloid particlescannot be impregnated deeply into the substrate and the imparted shapemay not be retained.

The heating temperature is from 100 to 500° C., preferably from 150 to500° C., and more preferably from 150 to 400° C.

The heating temperature is a temperature necessary for the dispersionmedium (typically water) of silicon dioxide colloidal solution toevaporate in a short time period, and may be appropriately determineddepending on the heating time period. The heating time period can beshortened by selecting a higher temperature for heating. When theselected heating temperature is 600° C. or higher, the hydroxyl groupsof the colloidal silica can react to form siloxane bonds. On the otherhand, when silica-based inorganic fiber containing a hydroxyl group,which is constituent of the fibrous board as the substrate, is heated upto 500° C. or more, the silica-based inorganic fiber is hardened. Thehardened silica fiber stimulates physical skin of a person who handlesthe silica-based inorganic fiber, and makes him feel itchy. This causespoor workability and handling property. Therefore, a temperature below500° C. is preferable for the heating temperature.

An appropriate pressure and an appropriate heating time period depend onthe form and average particle size of the colloidal particle, silicacontent in the colloidal solution, amount of coating, viscosity of thecolloidal solution, and the like.

In the case of using the silica colloid solution under theabove-mentioned conditions, the silica colloid solution can be cured byheating within 5 minutes, further within 3 minutes, yet further within 1minute. When heating and curing is insufficient, the imparted shapecannot be retained due to resilience restoring force of the fiber. Onthe other hand, heating and compressing for more than 5 minutes is notpreferred from the viewpoint of productivity.

Shapes to be imparted on the insulator includes a tray, hemisphere,pipe, semicircle in cross section, frustum, and the like. Besides them,another shape may be adopted.

As shown in FIG. 1, a compression molding method using a press platecorresponding to a male mold 5 is typically performed. A press andvacuum molding method and vaccum molding method are also adopted. Thepress and vacuum molding is carried out by clamping a flat board betweenthe female mold and the heated press plate, blowing air from the moldside to bring the flat board into contact with the heated press plate,thereby softening the flat board, and then stopping the blow-in of theair, followed by blowing compressed air from the press plate to pressthe board against the concave of the female mold. The vacuum molding iscarried out by clamping the flat board to a frame suspended above themold, heating and softening the flat board, and then making vacuum statebetween the flat board and the mold, thereby bringing the flat boardinto close contact with the mold, followed by cooling down to impart athree-dimensional shape.

In any method, it is preferable to press a colloidal silica-coatedsurface by the convex of the mold so that the coated surface become aconcave part of the molded body, which is a smaller stretch rate in amolded body having a configuration with concave and convex.

In the case of manufacturing a flat heat insulator, pressurizing with amold for shaping is not necessary. A heating and compressing step can bereplaced with solidification by drying the silica colloidal solution.However, heating is preferably conducted in order to shorten the timeperiod for drying and solidifying. Also pressurizing is preferablyconducted for stably holding the infrared mediator.

The particle dispersion type heat insulator and the three-dimensionallyshaped insulator are used so that the infrared mediator-held surface isplaced on the thermal source side. The infrared mediator absorbs thermalenergy (infrared rays, especially near-infrared rays) from the thermalsource and radiates it in the vicinity of the thermal source, therebythe consumption of the thermal energy of the thermal source can besuppressed.

<Metal Foil-Adhering Type Heat Insulator and Method for Manufacturing aThree-Dimensionally Shaped Insulator Article>

FIG. 2 is a diagram showing a configuration of one embodiment of themetal foil-adhering type heat insulator according to the invention. Ametal foil 4 is adhered to one surface (FIG. 2(a)) or both surfaces(FIG. 2(b)) of the substrate 1 through a silica cured product layer 3.The substrate 1 is a bulk of silica-based inorganic fibers containinghydroxyl groups.

In the metal foil-adhering type heat insulator, the metal foil 4 isadhered to the exterior surface of the insulator. Therefore, leakage ofinfrared rays to the surroundings may be suppressed thanks to thereflection by the metal foil 4 and excellent heat insulating performancemay be exhibited. In addition, covering the exterior surface with metalfoil can improve the handling property. In the case of the substratealone, there are problems: the fibers are readily broken when mountingthe substrate to a device; and powdery dust such as shots derived fromthe substrate scatters. However, covering the substrate's surface withthe metal foil can prevent scattering of the dust. Moreover, when themetal foil is positioned on the external side of the heat insulator, themetal foil can also prevent adhesion or intrusion of foreign matterssuch as dust and sand from the outside to the insulator.

A surface to be adhered should be selected according to thecharacteristic such as melting point of the metal foil and the usage ofthe heat insulator. For example, in the case of using aluminum foil(melting point of 660° C.), the metal foil-adhered surface should bepositioned on the external side of the insulator (opposite side to thethermal source) because the aluminum foil will be burnt off by exposureto a thermal source of 600° C. or more for a long time period.

If the temperature of the thermal source is equal to or lower than themelting point of the metal foil, the metal foil-adhered surface can bepositioned on the thermal source side.

Such a metal foil-adhering type heat insulator may be manufactured by amethod shown in FIG. 3. The method comprises a step of coating,applying, spraying or impregnating film-forming silica-based inorganicbinder on at least one surface of a flat substrate of silica-basedinorganic fibers containing hydroxyl group (FIG. 3(a)); a step ofattaching a metal foil 4 to a binder-coated surface (FIG. 3(b)); and astep of drying and solidifying the binder.

A metal foil-adhering type heat insulator having a plate- or sheet-likeshape can be produced by steps of applying binder, attaching a metalfoil, and drying and solidifying the binder. In the case ofmanufacturing a metal foil-adhering type heat insulator having athree-dimensional shape, the three-dimensional shape is imparted bypressing with a mold and solidifying the binder (FIG. 3(c)).

In other words, the metal foil-adhering type heat insulator having athree-dimensional shape is formed by a method similar to a method formanufacturing a particle dispersion type heat insulator. The methodcomprises a step of coating, applying, spraying, or impregnating afilm-forming silica-based binder 3′ to one surface of the flat substrate1; a step of attaching a metal foil 4 to the binder-coated surface; anda step of heating and compressing the flat substrate with molds 5′ and6′ for imparting a shape.

As is similar to the particle dispersion type heat insulator, examplesof the three-dimensional shape include tray, hemisphere, pipe,semicircle in cross section, frustum, and the like.

Each step will be described below.

(1) Binder Application Step

The application step is carried out by applying, coating, or sprayingthe above-mentioned film-forming silica-based binder (a silicapowder-dispersing fluid (suspension) or paste containing a layeredsilicate) 3′ to one side or both sides of a flat substrate 1 as afibrous board. The selection from the application techniques isappropriately done according to the viscosity and the solid content ofthe film-forming silica-based binder to be used.

A method for applying, coating, or spraying may be similar to that ofthe particle dispersion type heat insulating material. Spraying ispreferably adopted for workability and productivity. The film-formingsilica-based binder may be suitably diluted with water for spraying.

The amount of the binder to be coated is appropriately determinedaccording to the solid content of the binder. Accordingly, the amountranges from 100 to 600 g/m^(2,) preferably from 100 to 400 g/m², morepreferably 100 to 300 g)/m², in terms of solid content per coated areaof the substrate.

The binder cured product (silica cured product) has a higher thermalconductivity than the substrate. Therefore, if the amount (solidcontent) is too large, heat conduction of the silica cured product tendsto lower the heat insulating performance. On the other hand, if theamount is too small, the metal foil is insufficiently adhered to thesubstrate.

(2) Metal Foil-Adhering Step

A metal foil 4 is attached to the binder-coated surface of thesubstrate. In the case of pressing with a mold and solidifying a binder,a metal foil may be placed on a surface of the mold instead of thebinder-coated surface. In this case, the metal foil is pressed againstthe binder-coated surface of the substrate to attach the metal foil tothe substrate through the binder.

(3) Heating and Compressing Step

In the case of manufacturing a metal foil-adhering type heat insulatorhaving a three-dimensional shape, the metal foil-attached surface isheated and pressed with the molds 5′ and 6′ (FIG. 3(c)). For example,the mold is heated to a certain temperature and pressed against themetal foil-attached substrate at a certain pressure. The binder is driedand solidified in the heating and compressing step.

The pressure force and time period for heating and compressing forimparting a three-dimensional shape is similar to those in the case ofmanufacturing a particle dispersion type heat insulator. Accordingly,the pressure is such a force to reduce the thickness of the substrate byless than 40%, preferably between 5 and 35%, and more preferably between10 and 30%, based on the original thickness (100%). This reduction rateis correspondence to a reduction amount (T₁-T₂) wherein T₁ representsfor an original thickness of the substrate (FIGS. 3(a)) and T₂represents for the thickness of a resulting molded article (FIG. 3(d)).

A heating temperature and heating time period are appropriatelydetermined according to the kind and amount of the binder. The appliedpressure, especially the pressurizing speed, is selected with takinginto consideration the ductility of the metal foil because the ductilityis relevant to its molding followability.

Heating can shorten the time period for drying and solidifying, which ispreferable. On the other hand, rapid heating at a high temperature maycreate a porous cured product due to rapid evaporation of the dispersionmedium, resulting in lowering adhesive strength. The determination withrespect to heating temperature, heating time period, and whether heatingor non-heating may be appropriately done according to productivity andapplication of the metal foil-adhering type heat insulator.

In the case of FIG. 3, the metal foil 4 attached surface of thesubstrate is pressed by the male mold 5′. In the case that the metalfoil becomes the exterior surface of the hemispherical molded product, amale mold presses against the surface to which the metal foil is notattached. In this case, when the substrate is placed on the top of thefemale mold 6′, the surface without metal foil faces to the male moldinstead of the positioning shown in FIG. 3(c).

<A Combination Type Heat Insulator>

A combination type heat insulator is a heat insulator in which a metalfoil is adhered on one surface and an absorption type infrared mediatorsuch as ceramic particle is held on the other surface of the substrate.

Such a combination type heat insulator is set so that the absorptiontype infrared mediator-held surface is closer to the thermal source. Inthe combination type heat insulator, metal foil can prevent leakage ofinfrared rays and reflect the thermal energy toward the thermal source,while the ceramic particles can absorb the thermal energy from thethermal source and emit it in the vicinity of the thermal source. Thus,the consumption of thermal energy can be suppressed. Accordingly, thecombination type heat insulator is useful as a heat insulator forinsulation of a thermal source at high temperatures.

<Three-Dimensionally Shaped Insulator>

Thus manufactured heat insulator having a three-dimensional shape canstably retain the three-dimensional shape thanks to the silica curedproduct. That is, although the silica fiber substrate is difficult tostably retain the shape due to resilience restoring of the fibers, thesolidified binder or silica cured product can suppress the spring backbecause the silica cured product is not deformable. Therefore, the fiberconstituting the substrate is not needed to be fused at a hightemperature in the manufacturing method of the invention.

Both types of molded heat insulators (i.e. metal foil-adhering type heatinsulator and particle dispersion type heat insulator) have a thicknessof usually 3 to 20 mm, and more preferably 4 to 15 mm, although itdepends on the original thickness of the flat substrate (fibrous board).A heat insulator having such a thickness can assure a heat insulatingperformance required in lightweight applications.

The density of the molded heat insulator is 100-300 kg/m³, morepreferably 130-270 kg/m³. A low density means that the quantity offibers contained in the molded heat insulator is low, which tends tolower heat insulating performance. On the other hand, a high densitymeans that the fibrous substrate is excessively compressed. Compressionabove 300 kg/m³ introduces the resilience restoring of the fibers, whichlowers the retention of the shaped heat insulator.

The high temperature-heat insulator of the invention may be used notonly as a heat insulator but also as an acoustic absorber or a shockabsorber used at high temperatures, according to the thickness, density,and kind of fibers constituting the substrate. This is because the heatinsulator may exhibit a damping effect through gaps between entangledfibers in the substrate.

The heat insulator of the invention is resistant to 600° C. or more andfurther 800-1000° C. The heat insulator is excellent in heat insulatingproperty at high temperatures and can absorb and damp noise orvibration. Therefore, the heat insulator may be useful for an acousticabsorber mounted on exhaust portion in an automotive, especially mountednear manifold. Such application of the heat insulator may suppress atemperature drop when stopping the engine, and improve the reactionefficiency of the catalytic converter used at a high temperature, aswell as improve the engine efficiency. Also, improvement of fuelefficiency of a device operating at high temperatures such as a fuelcell may be expected by use of the heat insulator. A conventional heatinsulating sheet has to wrap around a device for insulation, however,workability in mounting operation may be reduced by using a threedimensionally shaped heat insulator having a recessed portion which fitsto the mounting portion of the device.

EXAMPLES [Comparison of High Temperature-Heat Insulators in HeatInsulating Performance] 1. Elements of High Temperature-Heat Insulator(1) Substrate

A needle-punched mat which is a fibrous mat (length: 300 mm, width: 300mm, thickness: 6 mm) produced by needle-punching a bulk of BELCOTEX®110from BELCHEM GmbH (composition:AlO_(1.5).18[(SiO₂)_(0.6)(SiO_(1.5)Oh)_(0.4)], fiber diameter: 9 μm,average fiber length: about 90 mm) was used.

(2) Infrared Mediator (2-1) Reflection Type Infrared Mediator

Aluminum foil having a thickness of 25 μm, “my foil” (trade name) fromUACJ Co. Ltd., was used.

(2-2) Absorption Type Infrared Mediator

SiC powder (Nippon Keical Limited), which had a particle sizedistribution D₅₀ of 1.8 μm and D₉₀ of 6.8 μm as measured by lightscattering method, was used. The emissivity of the SiC powder is about0.82.

(3) Raw Materials for Silica Cured Product (3-1) Film-FormingSilica-Based Binder

As the silica powder-dispersing fluid, heat-resistant inorganic adhesiveavailable from Sakai Chemical Corporation, which is an alkaline viscouspaste (crystalline silica of about 50%, sodium silicate of about 20%,viscosity of 20 to 50 Pa·s), was used. This heat-resistant inorganicadhesive was diluted with water (1:1 in weight ratio). Subsequently, asa film-forming component, “Sumecton SA”™ (synthetic clay classified intosmectite) from Kunimine Industries Co. Ltd. was added and stirredhomogenously to prepare a film-forming silica-based binder having aconcentration of 2 wt % of the “Sumecton SA”™.

(3-2) Colloidal Silica (Silica Colloid Solution)

As a binder, “Snowtex XS”™ from Nissan Chemical Corporation was used.“Snowtex XS”™ is a neutral colloidal solution in which silica sphericalparticles having average particle diameter of 4 to 7 μm are dispersed inaqueous dispersion medium (containing Na ion), and having 20% in SiO₂content.

2. Production of High Temperature-Heat Insulator (1) Metal Foil-AdheringType Heat Insulator (Nos. 1 and 2)

The film-forming silica-based binder prepared above was sprayed on onesurface of the above-mentioned needle-punched mat as a substrate with anautomatic gun. The amount of the film-forming silica-based bindersprayed on the surface was 333 g/m².

An aluminum foil (thickness: 25 μm) was placed on a binder-coatedsurface and a press plate heated at 300° C. was pressed against for 1minute. The pressure reduced the thickness of the mat by 35%, which iscorrespondence to 65% of the final thickness (T₂) of the mat, if themat's original thickness (T₁) is 100%. The substrate was pressed for 1minute, and then the press plate was released. Thus, a metalfoil-adhering type heat insulator Nos. 1 and 2 in which a metal foil isadhered on the one surface was prepared.

The heat insulating performance of the prepared heat insulator wasevaluated in accordance with a method described later. The results areshown in Table 1.

(2) Particle Dispersion Type Heat Insulator (Nos. 3 through 5)

An absorption type infrared mediator, SiC powder, was added to colloidalsilica to prepare SiC-containing silica colloid solution in such amanner that the solid content was 5% by weight, 10% by weight, or 15% byweight based on the weight of SiC-containing silica colloid solution.

The prepared three SiC-containing silica colloid solutions each wassprayed on one surface of a needle-punched mat (substrate) using anautomatic gun. The amount of the SiC-containing silica colloid solutionsprayed on the surface was 333 g/m². The same amount was sprayed despiteof differing in silica content of the SiC-containing silica colloidsolution.

After spraying the binder, a press plate heated at 300° C. was pressedagainst the substrate to reduce the thickness of the mat by 35%, whichis correspondence to 65% in the thickness (T2) of the compressed matrelative to the original thickness (T₁) which is 100%. This compressionstate was kept for 1 minute, and thereafter, the press plate wasreleased to prepare a particle dispersion type heat insulator No. 3-5 inwhich the infrared mediator was held on the one surface.

The heat insulating performance of thus prepared heat insulator wasevaluated in accordance with a method described later. The results areshown in Table 1.

(3) Combination Type Heat Insulator Comprising Metal Foil and CeramicPowder (Nos. 6 through 8)

The SiC-containing silica colloid solution prepared above was sprayed onone surface of a needle-punched mat as a substrate using an automaticgun. The amount of the SiC-containing silica colloid solution sprayed onthe surface was 333 g/m². The same amount was sprayed despite ofdiffering in silica content of the silica colloid solution. Afilm-forming silica-based binder was sprayed on the other surface of thesubstrate using an automatic gun, and then an aluminum foil was adheredto the binder-coated surface.

In such a state, a press plate heated at 300° C. was applied in the samemanner as No. 1. SiC was held on the one surface, and a metal foil wasadhered on the other surface of the substrate, and thereby combinationtype heat insulators Nos. 6-8 were prepared.

The heat insulating performance of thus prepared heat insulators wereevaluated in accordance with a method described later. The results areshown in Table 1.

(4) Reference Examples 1 and 2

A substrate alone was compressed in the same manner as No.1 to prepare aheat insulator, which was Reference example 1.

A substrate was sprayed with the sole colloidal silica (i.e. silicacolloid solution without SiC) and compressed in the same manner as No.3to prepare a heat insulator, which was Reference example 2.

The heat insulating performance of thus prepared heat insulators werealso measured and evaluated. The results are shown in Table 1.

3. Evaluation of Heat Insulating Performance

The heat insulating performance of the prepared high temperature-heatinsulators Nos. 1 to 8 and the reference examples 1 and 2 were evaluatedwith the measuring apparatus shown in FIG. 4

A furnace 10 had an opening 10 a with a diameter of 100 mm at the centerof its top surface, and a heater 11 was set in the furnace 10. Aprepared heat insulator 13 was placed on the top surface including theopening 10 a. The infrared mediator contained in the heat insulator 13was positioned on the thermal source side (furnace side) or the externalside, as shown in Table 1. A metal (SUS304) plate 14 (150 mm in length,150 mm in width and 1.5 mm in thickness) as a load was placed on theupper surface (external side) of the heat insulator 13. The metal plate14 was coated with black body-spray (emissivity of 0.94) available fromIchinen TASCO Co. Ltd.

The inside of the furnace 10 was heated by the heater 11 whosetemperature was controlled at 600° C. or 900° C. with a thermocouple 12.After reaching the intended heating temperature, it was allowed to standfor 30 minutes, and the surface temperature on the metal plate 14 wasmeasured with a thermocamera (FLIR 640 T). The measurement results areshown in Table 1.

TABLE 1 surface conditions furnace temperature thermal external (° C.)No source side side 600 900 Reference — — 176 303 example 1 ReferenceColloidal — 190 303 example 2 silica-coated 1 Aluminum — 142 —foil-adhered 2 — Aluminum 209 263 foil-adhered 3 SiC-coated — 188 286 (5wt %) 4 SiC-coated — 188 288 (10 wt %) 5 SiC-coated — 192 293 (15 wt %)6 SiC-coated Aluminum 216 274 (5 wt %) foil-adhered 7 SiC-coatedAluminum 212 270 (10 wt %) foil-adhered 8 SiC-coated Aluminum 215 269(15 wt %) foil-adhered

As for the heat insulator No. 1, the surface temperature when heated at900° C. could not be measured because the aluminum foil was burnt off.

As for the heat insulators Nos. 2 to 8, the heat insulating effect wasnot recognized as compared with the substrate alone (referenceexample 1) when heated at 600° C. However, the heat insulating effect ofheat insulator Nos. 2 to 8 each was recognized as compared with thesubstrate alone when heated at 900° C.

By comparison of Nos. 3-5 with Nos. 6-8, it is understood thatcombination of the absorption type infrared mediator and the reflectiontype infrared mediator can provide a higher heat insulation effect thanthe case of sole use of the absorption type infrared mediator.

In the case of insulation for a thermal source having a highertemperature, the positioning of the absorption type infrared mediator onthe thermal source side and the reflection type infrared mediator on theexternal side could provide an enhanced heat insulation effect.

[Relationship between Silica Colloid Particles and Three-DimensionalShape Moldability]

1. Elements of High Temperature-Heat Insulator (1) Substrate

A needle-punched mat (size: 300 mm length, 300 mm width, 6 mmthickness), “isoTHERM”® BCT from Frenzelit GmbH was used.

The needle-punched mat was a fiber mat with a thickness of nominally 6mm produced by needle-punching a bulk of BELCOTEX®110 from BELCHEM GmbH(composition: AlO_(1.5).18[(SiO₂)_(0.6)(SiO_(1.5)OH)_(0.4)], fiberdiameter: 9 μm).

(2) Colloidal Silica

The used colloidal silica had an average particle size and shape asindicated in Table 2. All colloidal silica in Table 2 are Na typeSNOWTEX® from Nissan Chemical Corporation, which is a suspension inwhich colloidal particles are stabilized with Na ion.

The chain-like aggregate in Table 2 was an aggregate of silica particles(primary particle diameter of 9 to 15 nm) gathering in a form of thread.The beads-like aggregate was an aggregate of silica particles (primaryparticle diameter of 18 to 25 nm). Their average particle sizesindicated in Table 2 was correspondence to a particle size of thesecondary colloidal particle measured by the dynamic light scatteringmethod.

2. Production of a Heat Insulator having a Three-Dimensional Shape Nos.11 through 17

The colloidal silica indicated in Table 2 was sprayed on one surface ofthe needle-punched mat. The amount of the colloidal silica was 666 g permeter square of sprayed surface. This amount of coating wascorrespondence to the solid content of 133-320 g/m².

Next, as shown in FIG. 1(b), the colloidal silica-coated substrate 1 wasplaced on the female mold 6 heated at 300° C. The colloidalsilica-coated surface was positioned on the upper side of the substrateand pressed for one minute with the male mold 5 heated at 300° C. Thepressure applied to the substrate reduced its thickness by 35%, whichwas correspondence to 65% of the thickness (T₂) after compression if theoriginal thickness (T₁) before compression is 100%. The pressurizedstate was kept for 1 minute, and then the male mold (press plate) 5 wasreleased to prepare a tray-shaped insulator 7 as shown in FIG. 1(c). Thedistance (d1) between the sidewalls of the insulator 7 immediately aftermolding was 150 mm, and the inclination angle α of the sidewall was 70°.The inclination angle α is an angle of the sidewall to the horizon.

The shape retention property and the handling property of thetray-shaped insulator was evaluated in accordance with methods describedlater. The results are also shown in Table 2.

Reference Examples 11 and 12

Reference Examples 11 and 12 were formed into a tray without colloidalsilica. That is, the substrate alone was compressed and heated at 300°C. for one minute (Reference example 11) or 5 minutes (Reference example12). The thickness of the substrate was reduced by 35% based on theoriginal thickness of 100%, which is correspondence to 65% in thethickness after compression.

The shape retention property and the handling property of the preparedtray-shaped insulators were evaluated. The results are also shown inTable 2.

3. Evaluation Method and Result (1) Shape Retention Property

As shown in FIG. 5, the bottom face of the tray-shaped insulator 20 wasfixed and the sidewall of the insulator 20 was touched to a guide rollerwith a load (W). The sidewall was inclined by the weight of the load(W). FIG. 5 also shows an inclined state of the tray-shaped insulator20′. For the load, a bearing roller having a diameter of 32 mm was usedand positioned at 34 mm in height from the bottom face of the insulator20. The sidewall sloped toward the horizon with the horizontal movementof the bearing roller. A displacement distance x (unit: mm) of thebearing roller was measured, and was adopted as an indicator of theslope. Shape retention property was evaluated according to the followingcriteria. The measurement was conducted on three insulators, and theaverage displacement distance of the measurement values were adopted inthe evaluation.

-   -   Best (⊚): the displacement distance per 10 g is less than 1 mm    -   Good (◯): the displacement distance per 10 g ranges from 1 mm to        below 2 mm    -   No problem (Δ): the displacement distance per 10 g ranges from 2        mm to 3 mm    -   Bad (×): the displacement distance per 10 g is more than 3 mm

(2) Handling Property

The colloidal silica coated-surface of a produced insulator was visuallyobserved and the quantity of powder as a cause of dust was examined onthe basis of visual observation. Further, the degree of adhered powderwere examined by touching the colloidal silica-coated surface andthereafter observing the hand.

If a relatively large quantity of powder was observed and the powderadhered to the hand is conspicuous level, the evaluation result wasrepresented as “Δ”. If the powder was observed but the quantity ofpowder adhered to the hand was not problematic, the evaluation resultwas represented as “◯”. In the case of no powder, the evaluation resultwas represented as “⊚”.

TABLE 2 No Reference Reference 11 12 13 14 15 16 17 example 11 example12 Silica Silica individual individual individual individual individualchain- beads- binderless binderless colloid particle dispersiondispersion dispersion dispersion dispersion like like solution of of ofof of aggregate aggregate spherical spherical spherical sphericalspherical particles particles particles particles particles average 4-610-15 10-15 20-25 20-25 40-100 80-120 — — particle size (nm) solid 20 2030 48 24 20 20 — — content (%) Heating and 1 min. 1 min. 1 min. 1 min. 1min. 1 min. 1 min. 1 min. 5 min. compressing time (min) Evaluation shape◯ Δ~◯ Δ~◯ Δ~◯ Δ ⊚ ◯ X Δ retention property handling ◯ ◯ ◯ X ◯ Δ Δ — ⊚property

As can be seen from the comparison of Nos. 11, 12, and 15, the shaperetention of the molded insulator was lowered with increase of theaverage particle diameter of the colloidal particles.

The use of chain-like aggregate of colloidal silica (No. 16) had atendency of higher shape retention property than the use of individuallydispersed spherical particles of colloidal silica. However, the quantityof powder remained on the surface of the insulator and adhered to thehand were increased in the case of the aggregate-type colloidal silica,which means poor handling property (Nos. 16 and 17).

Heating and compressing without colloidal silica for one minute couldnot retain the imparted tray shape. Extension of the heating andcompressing time period to 5 minutes made it possible to impart a trayshape in the absence of colloidal silica and retain the shape, but theshape retention property was inferior as compared to the case of thepresence of colloidal silica.

With respect to the obtained tray-shaped insulator No. 11 and Referenceexample 11, the surface of the recessed part of each shaped insulatorwas observed with a microscope (magnification: 500) and imaged as shownin FIGS. 6 and 7. From the comparison between FIG. 6 (No. 11) and FIG. 7(Reference example 11), it was confirmed that the colloidal silica had arole of connecting fibers to each other because the crosslinkage betweenfibers was observed in FIG. 6. Further, in FIG. 6, crosslinking withcolloidal silica was often observed in a colloidal silica-coated surfacelayer, but not hardly observed inside the substrate.

(4) Reference Example 13

An isocyanate (block polyisocyanate “Blonate®” from Daiei Sangyo Kaisha.Ltd.) was used instead of colloidal silica. The isocyanate was sprayedon one surface of the needle-punched mat in an amount of 30% by weightbased on the weight of the mat, followed by heating and compressing themat under the same conditions as No. 11. The release of the resultingmolded insulator from the male mold was troublesome due to adhesion tothe convex surface of the male mold. Ripping off the molded insulatorfrom the male mold, some fibers derived from the substrate were adheredto the convex surface of the male mold.

[Production of a Metal Foil-Adhering Type Heat Insulator]

A film-forming silica-based binder prepared for the heat insulator No. 1was sprayed on one surface of the needle-punched mat with an automaticgun. The amount of the film-forming silica-based binder sprayed on thesurface was 333 g/m². A metal foil 4 (thickness: 25 μm) was attached toa binder coated surface.

Thereafter, as shown in FIG. 3(c), the metal foil-attached mat wasplaced on the top of the female mold 6′ heated at 300° C., so that themetal foil 4 was positioned at upper side. The male mold 5′ mounted overthe female mold 6′ was heated at 300° C. and pressed against the metalfoil 4 for one minute. The applied pressure reduced the thickness of themat by 35%, which is correspondence to 65% of the thickness (T₂) aftercompression based on the original thickness (T₁) as 100%. After keepingthe compression state for one minute, the male mold (heated press plate)was released to obtain a tray-shaped heat insulator as shown in FIG. 8.The obtained heat insulator had α=70° and β=85° in inclination anglewhich is an angle of the sidewall of the tray-shaped insulator to thehorizon.

A photograph of the obtained tray-shaped insulator is shown in FIG. 9.The alminum foil was adhered uniformly to the interior surface of thetray-shaped substrate. Accordingly, the manufacturing method of theinvention can impart a stable tray shape on the fibrous substrate.

INDUSTRIAL APPLICABILITY

A high temperature-heat insulator of the invention exhibits excellentheat insulating performance at high temperatures such as 600° C. orhigher based on a silica-based inorganic fiber mat as a substrate and aninfrared mediator held in a surface part of the substrate. Since theinventive heat insulator exhibits heat resistance inherent in theinorganic fiber as an element of the heat insulator, the heat insulatoris useful for insulation of a device such as a catalytic converterrequired to maintain for high temperatures, as well as an acousticabsorbent and shock absorber used at high temperatures.

Furthermore, a method for manufacturing a three-dimensional shapedarticle of the invention can produce a molded article having athree-dimensional shape fitting to an exterior shape of the mountedportion in a short time of less than 5 minutes. Accordingly, theproductivity can be improved in a manufacturing site for forming into adesigned shape. Also it is useful for a user to mount the shaped articleon a target device. The shaped insulator can be directly mounted to astructure such as a muffler of an automotive and a fuel cell, andtherefore the labor load at a job site is reduced.

Moreover, when a metal foil is used as an infrared mediator, the metalfoil can prevent scattering of dust, powder and/or very short fiberderived from silica-based inorganic fiber substrate. Also, the metalfoil can prevent adhesion or intrusion of foreign matters from thesurroundings to the insulator. Therefore, the heat insulator of theinvention is useful for heat insulation for a structure used at hightemperatures and exposed to dust in the surroundings, such as aconstruction, a muffler or silencer of an exhaust system of anautomotive.

DESCRIPTION OF CODE

-   1 substrate-   1 a silica fiber-   2 ceramic powder-containing silica colloid solution-   3 silica cured product-   3′ film-forming silica-based binder-   4 metal foil-   7, 7′ three-dimensionally shaped insulator

1. A high temperature-heat insulator comprising a substrate comprising of a bulk of silica-based inorganic fiber containing a hydroxyl group; a metallic or ceramic infrared mediator held on at least a part of one surface of the substrate; and a silica cured product holding the infrared mediator on/in the substrate.
 2. The high temperature-heat insulator according to claim 1, wherein the infrared mediator is a metal foil having a thermal emissivity of 0.3 or less or a ceramic particle having a thermal emissivity of 0.6 to 0.9.
 3. The high temperature-heat insulator according to claim 1, wherein the infrared mediator is a metal foil having a thermal emissivity of 0.3 or less, and the silica cured product is a solidified material containing a layered silicate and silica powder.
 4. The high temperature-heat insulator according to claim 3, wherein the layered silicate is smectite.
 5. The high temperature-heat insulator according to claim 3, wherein the metal foil is an aluminum foil having a thickness of 5 to 150 μm.
 6. The high temperature-heat insulator according to claim 3, wherein the metal foil is held on one surface of the substrate, and the other surface of the substrate faces a thermal source to be insulated.
 7. The high temperature-heat insulator according to claim 2, wherein the infrared mediator is a ceramic particle having a thermal emissivity of 0.6 to 0.9, and the silica cured product is an inorganic polymer containing siloxane bond.
 8. The high temperature-heat insulator according to claim 7, wherein the ceramic particle has an average particle diameter of 0.5 to 4 μm.
 9. The high temperature-heat insulator according to claim 7, wherein the ceramic particle is carbide, nitride or boride of silicon.
 10. The high temperature-heat insulator according to claim 7, wherein the ceramic particle is held in/on one surface of the substrate, and the surface faces a thermal source to be insulated.
 11. The high temperature-heat insulator according to claim 1, wherein the substrate is a nonwoven fabric or mat, both in which the silica-based inorganic fibers are entangled, or a three-dimensionally shaped molded article of the nonwoven fabric or mat.
 12. A method for manufacturing a high temperature-heat insulator having a three-dimensional shape from a flat substrate of a silica-based inorganic fiber containing a hydroxyl group, comprising: providing the flat substrate with an infrared mediator by: coating, applying, spraying or impregnating a colloidal solution in which amorphous silica particles and particulate infrared mediator are dispersed in an aqueous medium, and/or coating, applying, spraying or impregnating a suspension or paste each containing a film-forming component and silica powder, on one surface of the flat substrate, and thereafter attaching a film-like infrared mediator to the surface; and heating and compressing the flat substrate to form into a three-dimensional shape.
 13. The manufacturing method according to claim 12, wherein a pressure applied in compressing is a pressure for reducing a thickness of the substrate by the range of 5% or more to less than 50% as compared to a thickness of the substrate before compression.
 14. The manufacturing method according to claim 12, wherein the temperature in the heating is in the range of 100 to 500° C.
 15. The manufacturing method according to claim 12, wherein a time period in the step of heating and compressing is less than 5 minutes.
 16. The manufacturing method according to claim 12, wherein the colloidal solution is a solution in which the amorphous silica particles/aggregate having an average particle size of 1 to 120 nm are dispersed as a dispersoid in the aqueous medium.
 17. The manufacturing method according to claim 12, wherein the silica particles in the colloidal solution are dispersed as an individual spherical silica particle having an average particle diameter of 4 to 18 nm in the aqueous medium.
 18. The manufacturing method according to claim 12, wherein the silica particles form a chain-like or branched aggregate in the aqueous medium, and the silica particle has an average particle diameter of 4 to 18 nm. 